Effect of crystallization on the lamellar orientation in thin films of symmetric poly(styrene)-b-poly(L-lactide) diblock copolymer

The effect of crystallization on the lamellar orientation of poly( styrene)-b-poly(L-lactide) (PS-PLLA) semicrystalline diblock copolymer in thin films has been investigated by atomic force microscopy (AFM), transmission electronic microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). In the melt state, microphase separation leads to a symmetric wetting structure with PLLA blocks located at both polymer/substrate and polymer/air interfaces. The lamellar period is equal to the long period L in bulk determined by small-angle X-ray scattering (SAXS). Symmetric wetting structure formed in the melt state provides a model structure to study the crystallization of PLLA monolayer tethered on glassy (T-c < T-g,T-PS) or rubber (T-c > T-g,T-PS) PS substrate. In both cases, it is found that the crystallization of PLLA results in a "sandwich" structure with amorphous PS layer located at both folding surfaces. For T-c <= T-g,T- PS, the crystallization induces a transition of the lamellar orientation from parallel to perpendicular to substrate in between and front of the crystals. In addition, the depletion of materials around the crystals leads to the formation of holes of 1/2 L, leaving the adsorbed monolayer exposure at the bottom of the holes.

Study on the origin of inverted phase in drying solution-cast block copolymer films

In a previous study, we reported observation of the novel inverted phase (the minority blocks comprising the continuum phase) in kinetically controlled phase separating solution-cast poly(styrene-b-butadiene-b-styrene) (SBS) triblock copolymer films [Zhang et al. Macromolecules 2000, 33, 9561-7]. In this study, we adopt the same approach to investigate the formation of inverted phase in a series of solution-cast poly(styrene-b-butadiene) (SB) asymmetric diblock copolymers having nearly equal polystyrene (PS) weight fraction (about 30 wt %) but different molecular weights. The microstructure of the solution-cast block copolymer films resulting from different solvent evaporation rates, R, was inspected, from which the kinetically frozen-in phase structures at qualitatively different block copolymer concentrations and correspondingly different effective interaction parameter, chieff, can be deduced. Our result shows that there is a threshold molecular weight or range of molecular weight below which the unusual inverted phase is accessible by controlling the solvent evaporation rate. In comparing the present result with that of our previous study on the SBS triblock copolymer, we find that the formation of the inverted phase has little bearing on the chain architecture. We performed numerical calculations for the free energy of block copolymer cylinders and found that the normal phase is always preferred irrespective of the interaction parameter and molecular weight, which suggests the formation of the inverted phase to have a kinetic origin.

Synthesis and characterization of interpenetrating polymer networks based on polyacrylate and epoxy

The synthesis and properties of simultaneously interpenetrating networks (SINs) based on poly(polyethylene glycol diacrylate) (PEGDA) and epoxy (diglycidyl ether of bisphenol A, DGEBA) were studied. The effect of compositional variation on the morphology and properties of products was investigated. The swelling coefficient, densities, glass transition behavior, and thermal stability of these interpenetrating networks (IPNs) are discussed. Microphase separation morphological structures were found in all PEGDA/DGEBA IPNs. Decreased swelling ratios compared to the calculated swelling coefficients based on the weight additivity of the components were obtained after the formation of IPNs. Increased density and thermal stability were also obtained in these IPNs, implying the existence of interpenetration (topological entanglements) among the component networks.

MORPHOLOGY AND DYNAMIC MECHANICAL-PROPERTIES OF AB CROSS-LINKED POLYMERS BASED ON POLYURETHANES

Polyoxypropylene glycol (PPG) (or castor oil) and toluene diisocyanate (TDI) were mixed, and the prepolymer polyurethane (PU) (I) was formed. Vinyl-terminated polyurethane (II) was prepared from (I), and hydroxyethyl acrylate, AB crosslinked polymers (ABCPs) were synthesized from (II) and vinyl monomers such as styrene, methyl methacrylate, vinyl acetate, etc. The dynamic mechanical properties and morphology of ABCPs were measured. The ABCPs based on PPG have double glass transition temperatures (T(g)) on the sigma-vs. temperature curves. They display a two-phase morphology with plastic components forming the continous phase and PU-rich domains forming the separated phase on the electron micrographs. Irregular shapes and a highly polydisperse distribution of PU-rich domain sizes were observed. The crosslink density of ABCPs has a notable effect on the morphology and properties. The average diameter of the PU-rich domains depends on the molecular weight of prepolymer PPG. The highly crosslinked structures will produce large numbers of very small domains. ABCPs based on castor oil show a single T(g) relaxation on the dynamic mechanical spectra. The compatibility between the two components is much better in ABCPs based on castor oil than in those based on PPG, because there is a high crosslink density in the former. Comparison of the dynamic mechanical spectra of ABCP and interpenetrating networks (IPN) based on castor oil with similar crosslink density and composition imply that the two components in ABCP are compatible whereas microphase separation occurs in IPN. An improvement in the compatibility is achieved by the crosslinking between the two networks.

聚苯乙烯-聚（左旋-乳酸）嵌段共聚物薄膜的相分离与结晶

本论文以对称的半结晶型的聚苯乙烯-聚（左旋-乳酸）（PS-b-PLLA）嵌段共聚物薄膜为研究对象，通过在不同厚度的膜中的时间相关的相行为的演变，来研究不同界面对嵌段共聚物薄膜熔融状态的相结构的影响，并以此相结构为模版来研究软硬受限下结晶对相分离的影响。 首先，我们研究了在不同厚度膜中的熔融状态的相结构。通过调控膜的厚度及退火时间，实现片层方向的转变。随着膜厚的增加，由于选择性的聚合物/基板界面及中性的聚合物/空气界面的作用下，达到平衡态后片层方向由平行向垂直转变。当膜厚大于一个周期时，同一膜厚下，随着退火时间的增加，片层方向由平行向垂直转变。片层方向在由平行向垂直的转变时，形成平行与垂直共存的混合结构。 在熔融状态下得到结晶的PLLA在表面对称润湿的平行片层，以这种结构为模版，研究了系留在PS基板上的PLLA单层的结晶，以及结晶对相分离结构的影响。从有序的熔融状态结晶后，形成了上下非晶中间结晶的“三明治”结构，结晶结构为α晶型正交晶系，结晶分子链垂直于界面。当Tc ≤ Tg,PS, 时，由于分子链的活动性较差，而且 PS与PLLA具有相近的表面能，结晶诱导了垂直片层的形成。当Tc > Tg,PS, 由于分子链的活动性较强，没有形成垂直片层。 以中性的聚合物/空气界面作用下形成的垂直片层为模版，研究了软硬受限条件下结晶对垂直片层结构演变的影响。硬受限下，结晶没有破坏相分离结构，在微相分离的垂直片层中受限结晶，结晶后片层周期增加。软受限下，非晶的PS分子链的活动性较强，结晶破坏了原有的相分离结构，生成棒状结晶。由于受限，结晶结构较为特殊属于单斜晶系。 以平行与垂直片层共存的混合结构为模版，研究了结晶对此结构的影响，发现平行与垂直片层分别结晶形成不同的结晶形貌，两种结晶在形成的过程中相互影响。

PS-b-PEO嵌段共聚物薄膜的结晶与微相分离

半结晶性嵌段共聚物中，嵌段间的不相容性导致的微相分离与结晶嵌段的结晶行为之间存在相互竞争与协同作用。现阶段的大部分工作主要集中于半结晶性嵌段共聚物相分离发生后的结晶行为的结晶动力学和内部链折叠，而对于结晶与微相分离同时发生时的结晶与微相分离行为的研究还较少。 本论文以半结晶性的聚苯乙烯和聚环氧乙烷的二嵌段共聚物（PS-b-PEO）薄膜为研究对象，研究其破坏性（break out）结晶行为，以及研究方形片晶与微相分离结构的关系。 首先，本论文研究了不同相分离取向对结晶行为的影响。我们通过控制膜厚得到垂直基底和平行基底的微相分离薄膜。在溶剂蒸汽中，微相分离取向垂直基底时，仅仅是有序度增加，片晶协同生成。退火时间增加，结晶成核控制生长向扩散控制生长转变，导致片晶周围树枝晶生长。微相分离结构为平行基底取向时，焓主要用于取向转变和有序度增加，体系没有片晶生成，仅边缘效应使树枝晶产生。在结晶取向方面，研究了溶剂蒸汽氛围内界面作用改变使分子链轴垂直基底（flat-on）结晶向分子链轴平行基底（edge-on）结晶的转变。随着溶剂分子扩散到基底界面，结晶嵌段PEO与基底相互作用从强变弱，是发生这种转变的决定因素。 其次，从片晶与微相分离相互转变和片晶上微相分离刷的形成两方面研究片晶与微相分离的竞争与协同关系。退火溶剂的选择性影响片晶与微相分离的竞争。在PEO不良溶剂蒸汽环己烷中发生以下转变：片晶生成，逐渐被微相分离破坏，片晶重新生成；PEO良溶剂水中仅存在结晶到微相分离的转变。即晶体溶解，与PS发生微相分离以获得能量上的有利状态。可溶解嵌段的自由体积增加和结晶嵌段的低溶胀性分别是微相分离和结晶发生的关键因素。片晶与微相分离协同关系研究上，通过调控二嵌段共聚物片晶上聚合物刷的密度（小于14.3大于3.8），获得具有微相分离结构的聚合物刷。PS-PS刷的弱相互作用以及PS与PEO（连接PEO片层结构未结晶的PEO链）之间的强不相容性对片层上微相分离刷的形成起来决定作用。

溶剂诱导嵌段共聚物薄膜的微观相分离

通过研究发现薄膜厚度、溶剂对不同链段的选择性以及溶剂蒸汽处理时间对嵌段共聚物薄膜表面形态的演变有重要影响。对于对称双嵌段共聚物（PS-b-PMMA）薄膜在薄膜厚度小于0.5L_o时，在PMMA的选择性溶剂中处理不同时间时，除了得到垂直的lamellae形态外，还得到了有序纳米孔洞以及有序纳米孔洞和片层共存的新形态。同时其表面组成发生了变化，由最初PS位于表面层而转变为PMMA位于表面层。更进一步，得到的纳米结构图案化的薄膜具有环境敏感性。当将其置于对PS嵌段具有选择性的溶剂蒸汽中时，表面形貌发生了反转。另外研究发现，二元双嵌段共聚物共混体系，即小分子量的PS-b-PMMA和大分子量的PS-b-PMA共混，在硅基底上发生自组装形成具有有序孔洞结构的薄膜。这种结构完全不同于某一组分单独存在时所形成的微相结构。根本原因在于PMA和PMMA嵌段化学结构上的相似性，使PMMA链部分嵌入能量上优先吸附于极性基底的PMA嵌段中，形成了两种分子中的PS相容在一起构成的连续相围绕着塌陷的PMMA相的形态。

半结晶性嵌段共聚物自组装与薄膜微相分离

本论文以半结晶性的PLLA-b-PS为研究对象，主要研究两个方面的问题。首先研究聚合物结晶对嵌段共聚物在稀溶液中的自组装行为的影响。在此基础上，研究薄膜状态下，聚合物结晶与微相分离之间的相互作用。首先，我们系统地研究了PLLA-b- PS在不同溶剂中的自组装结构。通过调节溶剂选择性由中性向弱选择性和选择性改变，PLLA-b-PS分别形成类旋节图案，松散的胶束结构和典型的胶束核壳结构。使用混合溶剂，实现了从结晶性的球形胶束向结晶性的片状胶束的转变。标度理论分析和实验结果表明，溶剂与胶束结晶核心之间的界面能的增加是发生这一转变的主要原因。为了研究薄膜中的微相分离与结晶之间的相互作用，我们比较了三种薄膜条件下的相分离与结晶过程。均匀平坦的PLLA-b-PS薄膜是旋节不稳定的，在几以上时，分子链发生微相分离，形成旋节图案，表面诱导分子链的伸展有序化过程促使PLLA分子链发生折叠结晶，形成非经典的亚稳态凸出结构，相分离层间距增大50％。结晶过程为一级动力学。在薄膜中引入成核剂时，PLLA在几以上即开始结晶，同时实现了PLLA与P3之间的相分离，薄膜的旋节不稳定性得到了松弛。结晶使薄膜收缩，形成大量的裂纹。在PLLA熔点以上时，以裂纹为核，在薄膜中形成大量的孔洞。孔洞的生长为经典的动力学过程。我们利用自组装方法在薄膜中引入半结晶性的开放的纳米棒。在几以上时，PLLA在纳米棒中发生结晶，诱导薄膜中的分子链向纳米棒迁移，从而在薄膜中形成孔洞结构。同时，薄膜中的未结晶分子链被表面和界面诱导取向，这种取向结构利于PLLA结晶，结晶被加速，从而孔洞的生长也被加速。也就是说，结晶与孔洞的生长相互促进。在相分离薄膜中，PLLA的结晶形态与结晶温度有关。To＜TgPS时，结晶被束缚在相结构中，相分离结构不变；TgPs＜Tc＜Tm以及Tc→Tm时，结晶对相结构有一定的破坏，相分离片层结构的层间距增大，薄膜收缩，形成大量的裂纹和缺陷。在180℃时，PLLA形成不稳定的晶体结构；PLLA与PS之间的相分离强度被减弱，在线张力作用下，岛状结构的相对高度大幅度增加；在岛状结构的边缘，线张力驱使部分分子链穿越已有的相结构，形成多层岛状结构。

Lattice Boltzmann study of hydrodynamic effects in lamellar ordering process of two-dimensional quenched block copolymers

By incorporating self-consistent field theory with lattice Boltzmann method, a model for polymer melts is proposed. Compared with models based on Ginzburg-Landau free energy, our model does not employ phenomenological free energies to describe systems and can consider the chain topological details of polymers. We use this model to study the effects of hydrodynamic interactions on the dynamics of microphase separation for block copolymers. In the early stage of phase separation, an exponential growth predicted by Cahn-Hilliard treatment is found. Simulation results also show that the effect of hydrodynamic interactions can be neglected in the early stage.

The phase behavior of comblike block copolymer A(m+1)B(m)/homopolymer A mixtures

The phase behaviors of comblike block copolymer A(m+1)B(m)/homopolymer A mixtures are studied by using the random phase approximation method and real-space self-consistent field theory. From the spinodals of macrophase separation and microphase separation, we can find that the number of graft and the length of the homopolymer A have great effects on the phase behavior of the blend. For a given composition of comblike block copolymer, increasing the number of graft does not change the macrophase separation spinodal curve but decreases the microphase separation region. The addition of a small quantity of long-chain homopolymer A increases the microphase separation of comblike block copolymer/homopolymer A mixture.

Square lamellar structure having phase-separated microdomain in H-shaped block copolymer thin film

The morphology of a H-shaped block copolymer (poly(ethylene glycol) backbone and polystyrene branches (PS)(2)PEG(PS)(2)) in a thin film has been investigated. A peculiar square lamella that has a phase-separated microdomain at its surface is obtained after spin coating. The experimental temperature plays a critical role in the lamellar formation. The copolymer first self-assembles into square lamellar micelles with an incomplete crystalline core due to the crystallizability of PEG.

Synthesis and characterization of phenylene-thiophene all-conjugated diblock copolymers

Grignard metathesis (GRIM) polymerization for all-conjugated diblock copolymers comprising poly (2,5-dihexyloxy-1,4-phenylene) (PPP) and poly(3-hexylthiophene) (P3HT) blocks were systematically studied with LiCl as additive and 1,2-bis (diphenylphosphino) ethane nickel dichloride (Ni(dppe)Cl-2) or 1,3-bis(diphenylphosphino) propane nickel dichloride (Ni(dppp)Cl-2) as catalyst. It was found that the addition order of the monomers was crucial for the success of copolymerization. With the monomer addition in the order of phenyl and then thienyl Grignard reagents, all-conjugated PPP-b-P3HT diblock copolymers with different block ratios were successfully synthesized. In contrast, the inverted addition order only afforded a mixture containing both block copolymers and deactivated or end-capped homopolymers.

Dendritic Superstructures and Structure Transitions of Asymmetric Poly(L-lactide-b-ethylene oxide) Diblock Copolymer Thin films

The evolution of morphologies of isothermally crystallized thin films with different thicknesses of poly(L-lactide-bethylene oxide) diblock copolymer was observed by optical microscopy (OM) and atomic force microscopy (AFM). Dendritic superstructures stacked with lamellae were investigated in thin films with similar to 200 nm to similar to 400 nm thickness. The lamellar structure was a lozenge- or truncated-lozenge-shaped single crystal of PLLA confirmed by AFM observations. The contour of the dendritic superstructures is hexagonal, and two types of sectors, [110] and [100], can be classified in terms of the chain-folding and crystal growth directions. These phenomena Are due to the interplay of the crystallization of the PLLA block, the microphase separation of the block copolymer, and the effect of the film thickness.

STUDY OF COARSENING OF MICRODOMAINS IN BLOCK COPOLYMERS BY LATTICE BOLTZMANN METHODS

In order to understand the coarsening of microdomains in symmetric diblock copolymers at the late stage, a model for block copolymers is proposed. By incorporating the self consistent field theory with the free energy approach Lattice Boltzmann model, hydrodynamic interactions can be considered. Compared with models based on Ginzburg-Landau free energy, this model does not employ phenomenological free energies to describe systems. The model is verified by comparing the simulation results obtained using this method with those of a dynamical version of the self consistent mean field theory. After that,the growth exponents of the characteristic domain size for symmetric block copolymers at late stage are studied. It is found that the viscosity of the system affects the growth exponents greatly, although the growth exponents are all less than 1/3 Furthermore, the relations between the growth exponent, the interaction parameter and the chain length are studied.

Hydrogen Bonding and Crystallization in Biodegradable Multiblock Poly(ester urethane) Copolymer

The hydrogen bonding and crystallization of a biodegradable poly(ester urethane) copolymer based on poly(L-lactide) (PLLA) as the soft segment were investigated by FTIR. On slow cooling from melt, the onset and the progress of the crystallization of the urethane hard segments were correlated to the position, width, and relative intensity of the hydrogen-bonded N-H stretching band. The interconversion between the "free" and hydrogen-bonded N-H and C=O groups in the urethane units in the process was also revealed by 2D correlation analysis of the FTIR data. The crystallization of the PLLA soft segments was monitored by the ester C=O stretching and the skeletal vibrations. It was revealed that the PLLA crystallization was restricted by the phase separation and the urethane crystallization, and at cooling rates of 10 degrees C/min or higher, the crystallization of the PLLA soft segments was prohibited.