Thermoplastic Elastomers Based on Compatibilized Poly(butylene terephthalate) Blends: Effect of Functional Groups and Dynamic Curing

Two sets of graft copolymers were prepared by grafting glycidyl methacrylate (GMA) or ally] (3-isocyanate-4-tolyl) carbamate (TAI) onto ethylene/propylene/diene terpolymer (EPDM) in an internal mixer. These graft copolymers were used as the compatibilizer to prepare the thermoplastic elastomers (TPEs) containing 50 wt%, of poly(butylene terephthalate), PBT, 30 wt% of compatibilizer, and 20 wt% of nitrile-butadiene rubber, NBR. The indirect, two-step mixer process was chosen for dynamic curing.

Preparation of fully cross-linked CNBR/PP-g-GMA and CNBR/PP/PP-g-GMA thermoplastic elastomers and their morphology, structure and properties

Binary CNBR/PP-g-GMA and ternary CNBR/PP/PP-g-GMA thermoplastic elastomers were prepared by reactive blending carboxy nitrile rubber (CNBR) powder with nanometer dimension and polypropylene functionalized with glycidyl methacrylate (PP-g-GMA). Morphology observation by using an atomic force microscope (AFM) and TEM revealed that the size of CNBR dispersed phase in CNBR/PP-g-GMA binary blends was much smaller than that of the corresponding CNBR/PP binary blends. Thermal behavior of CNBR/PP-g-GMA and CNBR/PP blends was studied by DSC. Comparing with the plain PP-g-GMA, T, of PP-g-GMA in CNBR/PP-g-GMA blends increased about 10degreesC. Both thermodynamic and kinetic effects would influence the crystallization behavior of PP-g-GMA in CNBR/PP-g-GMA blends. At a fixed content of CNBR, the apparent viscosity of the blending system increased with increasing the content of PP-g-GMA. FTIR spectrum verified that the improvement of miscibility of CNBR and PP-g-GMA was originated from the reaction between carboxy end groups of CNBR and epoxy groups of GMA grafted onto PP molecular chains. Comparing with CNBR/PP blends, the tensile strength, stress at 100% strain, and elongation at break of CNBR/PP-g-GMA blends were greatly improved.

Synthesis and characterization of network liquid crystal elastomers and thermosets

A new series of network liquid crystal polymers were synthesized by graft copolymerization of the difunctional mesogenic monomer 4-allyloxy-benzoyloxy-4'-allyloxybiphenyl (M) upon polymethylhydrosiloxane (PMHS). Monomer M acted not only as a mesogenic unit but also as a crosslinker for the network polymers. The chemical structures of the polymers were confirmed by IR spectroscopy. DSC, TGA, and X-ray scattering were used to measure their thermal properties and mesogenic properties. The glass transition temperature (T-g) of these network liquid crystal polymers was increased when the monomer was increased, and T-d (temperature of 5% weight loss) at first went up and reached a maximum at P, then went down. The slightly crosslinked polymers (P, P,) show rubber-like elasticity, so it was called liquid-crystal elastomer. Network polymers will lose elasticity property with a highly crosslinked degree, and turn into thermosetting polymers (P-4, P-5). All polymers exhibited a smectic texture by X-ray scattering.

Studies on water-swellable elastomers .2. Thermal properties and crystalline behavior of amphiphilic graft copolymers with poly(ethylene glycol) side chains

The thermal properties and crystalline structure of the amphiphilic graft copolymers CR-g-PEG600, CR-g-PEG2000, and CR-g-PEG6000 using chloroprene rubber (CR) as the hydrophobic backbone and poly(ethylene glycol) (PEG) with different molecular weights as the hydrophilic side chains were studied by DSC and WAXD. The results showed that a distinct phase-separated structure existed in CR-g-PEGs because of the incompatibility between the backbone segments and the side-chain segments. For all the polymers studied, T-m2, which is the melting point of PEG crystalline domains in CR-g-PEG, decreased compared to that of the corresponding pure PEG and varied little with PEG content. For CR-g-PEG600 and CR-g-PEG2000, T-m1, which is the melting point of the CR crystalline domains, increased with increasing PEG content when the PEG content was not high enough, and at constant PEG content, the longer were the PEG side chains the higher was the T-m1. The crystallite size L-011 of CR in CR-g-PEGs increased compared to that of the pure CR and decreased with increasing PEG content. (C) 1997 John Wiley & Sons, Inc.

A constitutive model for cavitation and cavity growth in rubber-like materials under arbitrary tri-axial loading

In this paper, we attempted to construct a constitutive model to deal with the phenomenon of cavitation and cavity growth in a rubber-like material subjected to an arbitrary tri-axial loading. To this end, we considered a spherical elementary representative volume in a general Rivlin's incompressible material containing a central spherical cavity. The kinematics proposed by [Hou, H.S., Abeyaratne, R., 1992. Cavitation in elastic and elastic-plastic solids. J. Mech. Phys. Solids 40, 571-722] was adopted in order to construct an approximate but optimal field. In order to establish a suitable constitutive law for this class of materials, we utilized the homogenisation technique that permits us to calculate the average strain energy density of the volume. The cavity growth was considered through a physically realistic failure criterion. Combination of the constitutive law and the failure criterion enables us to describe correctly the global behaviour and the damage evolution of the material under tri-axial loading. It was shown that the present models can efficiently reproduce different stress states, varying from uniaxial to tri-axial tensions, observed in experimentations. Comparison between predicted results and experimental data proves that the proposed model is accurate and physically reasonable. Another advantage is that the proposed model does not need special identification work, the initial Rivlin's law for the corresponding incompressible material is sufficient to form the new law for the compressible material resulted from cavitation procedure. (C) 2007 Elsevier Ltd. All rights reserved.

纳米耐油型全硫化热塑性弹性体的制备与形态、结构及性能研究

本文以过氧化物为引发剂，采用反应挤出的方法，制备了甲基丙烯酸缩水甘油酷官能化聚丙烯，采用化学滴定法和红外光谱法均证实了接枝共聚物的存在，并研究了反应条件对PP-g-GMA接枝率、接枝效率和熔体流动速率的影响，结果表明：1．当DCP含量一定时，随着单体含量的增加，接枝产物的接枝率出现了一个峰值。这表明一味地增加单体浓度未必有利于接枝率的提高；2．当GMA单体浓度一定时，PP-g-GMA的接枝率和熔融指数均随着引发剂含量的增加而逐渐增大，这表明引发剂浓度的增加在促进接枝反应的同时也引入了更多的副反应；3．助剂苯乙烯的加入大大地提高了PP-g-GMA的接枝率和接枝效率，且产物的熔融指数与纯聚丙烯相比变化很小，这表明助剂苯乙烯的加入有效地抑制了副反应的发生，且促进了接枝反应的发生。研究了官能化聚丙烯PP-g-GMA的形态、结构与性能，结果表明：1．官能化对聚丙烯的结晶行为有显著的影响，不仅结晶温度和熔融温度有显著的增加，而且结晶度也有一定程度的增加；2．纯聚丙烯的结晶结构为典型的a型结晶，而接枝聚丙烯的结晶则以a型结晶为主，并出现了少量的Y型结晶；3．采用Avrami方程可以很好的描述官能化聚丙烯的初级结晶行为，纯聚丙烯和官能化聚丙烯的 tl几和tmax均随着结晶温度的增加而增加，这表明它们的结晶过程由成核控制；4．采用Jeziornn法研究了官能化聚丙烯的非等温结晶动力学，非等温结晶过程可以分为初级结晶和次级结晶两部分，在次级结晶阶段，曲线偏离了初级结晶部分的直线，表明在次级结晶阶段，官能化聚丙烯的成核与生长方式发生了变化；5．采用DMA研究了官能化聚丙烯的动态热机械行为，官能化后聚丙烯的耐热性提高了，而且随着接枝率的升高，耐热性又有进一步的提高。以官能化聚丙烯作为反应型增容剂，采用反应共棍的方法，制备了耐油型全 硫化CNBR/PP热塑性弹性体，并研究了热塑性弹性体的形态、结构与性能。主要 结果如下：1．采用红外光谱法表征了梭基丁睛粉末橡胶和PP-g-GMA间的反应。 2．透射电子显微镜和原子力显微镜结果表明，当一部分聚丙烯被官能化聚丙烯替代后，体系中橡胶粒子的尺寸明显变小了，分布也更加均一了。在CNBR/PP-g-GMIA 体系中，原位增容反应形成的共聚物位于cNBR和PP-g-GMA两相的界面处。3．加入少量接枝聚丙烯后共混物的力学性能，如拉伸强度、100％定伸强度和断裂伸长 率均有明显的提高，而且，对于CNBR/PPPP-g-GMA共混物，只需少量的界面增 容剂便可以使两相界面达到饱和并达到较好的增容效果。4．动力学和热力学因素 均影响共混物中聚丙烯的结晶行为，在CNBR/PP体系中，动力学因素占主导地位，而CNBR/PP-g-GMA体系中热力学因素占主导作用。另外，采用Avromi方程描述了CNBR/PP和CNBR/PP-g-GMA体系的等温结晶动力学。5．接枝聚丙烯的加入阻碍了接枝聚丙烯与梭基丁睛橡胶两相间的界面层滑移，因此提高了体系的粘度。以官能化聚丙烯作为反应型增容剂，采用反应共混的方法，制备了耐油型全硫化NBR/PP热塑性弹性体，并研究了热塑性弹性体的形态、结构与性能。主要结果如下：1．采用红外光谱法表征了官能化聚丙烯与端氨基液体丁睛橡胶间的反应，但仅从红外光谱的结果很难断定产物的分子结构；2．采用透射电子显微镜观察了NBR/PP共混物的微观形态，结果表明，NBR／PP共混物体系中除了含有直径为几十纳米的小橡胶粒子外，还有直径为几微米甚至几十微米的大橡胶粒子存在，且随着橡胶含量的增加，体系中大橡胶粒子的数量增多了，小橡胶粒子的分布也变得密集了；3．采用差示扫描量热法表征了NB侧PP共混物的受限结晶行为，结果表明，（1）在220℃的高温下，部分丁睛橡胶分子产生了一定的运动，从而限制了聚丙烯分子的运动，使聚丙烯分子产生了受限结晶行为；（2）随着橡胶含量的增加，橡胶粒子间的距离逐渐变小，这使得位于橡胶粒子间隙的聚丙烯分子的运动受到限制，因此聚丙烯表现出受限结晶的行为；（3）受限的聚丙烯分子更倾向于Y型结晶。

Integrated processing-structure-property analysis on rubber in-mold vulcanization

On the basis of the quantitative relationship among rubber processing, structure and property, the methodology of the integrated processing-structure-property analysis on rubber in-mold vulcanization is presented, and then the temporal evolution and spatial distribution characteristics of silicone rubber hot processing parameters, crosslinking structure parameters and mechanical property parameters are obtained by means of the finite element method. The present work is helpful for optimizing curing conditions, and then the design of rubber vulcanization processes according to certain requirements can be done.

Preparation of a blocked isocyanate compound and its grafting onto styrene-b-(ethylene-co-1-butene)-b-styrene triblock copolymer

The epsilon-caprolactam was used to block the isocyanate group to enhance the storage stability of allyl (3-isocyanate-4-tolyl) carbamate. The spectra of FTIR and NMR showed that blocked allyl (3-isocyanate-4-tolyl) carbamate (BTAI) possesses two chemical functions, an 1-olefin double bond and a blocked isocyanate group. The FTIR spectrum showed BTAI could regenerate isocyanate group at elevated temperature. DSC and TG/DTA indicated the minimal dissociation temperature was about 135 degrees C and the maximal dissociation rate appeared at 226 degrees C. Then the styrene-b-(ethylene-co-1-butene)-b-styrene triblock copolymer (SEBS) was functionalized by BTAI via melt free radical grafting. The effect of temperature, monomer and initiator concentrations on the grafting degree and grafting efficiency was evaluated. The highest grafting degree was obtained at 200 degrees C. The grafting degree and grafting efficiency increased with the enhanced concentration of BTAI or initiator.

Thermal analysis of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) irradiated under vacuum

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) was irradiated by Co-60 gamma-rays (doses of 50, 100 and 200kGy) under vacuum. The thermal analysis of control and irradiated PHBV, under vacuum was carried out by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The tensile properties of control and irradiated PHBV were examined by using an Instron tensile testing machine. In the thermal degradation of control and irradiated PHBV, a one-step weight loss was observed. The derivative thermogravimetric curves of control and irradiated PHBV confirmed only one weight-loss step change. The onset degradation temperature (T-o) and the temperature of maximum weight-loss rate (T-p) of control and irradiated PHBV were in line with the heating rate (degreesC min(-1)). T-o and T-p of PHBV decreased with increasing radiation dose at the same heating rate. The DSC results showed that Co-60 gamma-radiation significantly affected the thermal properties of PHBV. With increasing radiation dose, the melting temperature (T-m) of PHBV shifted to a lower value, due to the decrease in crystal size. The tensile strength and fracture strain of the irradiated PHBV decreased, hence indicating an increased brittleness.

Morphologies in solvent-annealed thin films of symmetric diblock copolymer

We have systematically studied the thin film morphologies of symmetric poly(styrene)-block-poly(methyl methacrylate) (PS-b-PMMA) diblock copolymer after annealing to solvents with varying selectivity. Upon neutral solvent vapor annealing, terraced morphology is observed without any lateral structures on the surfaces. When using PS-selective solvent annealing, the film exhibits macroscopically flat with a disordered micellar structure. While PMMA-selective solvent annealing leads to the dewetting of the film with fractal-like holes, with highly ordered nanoscale depressions in the region of undewetted films. In addition, when decreasing the swelling degree of the film in the case of PMMA-selective solvent annealing, hills and valleys are observed with the coexistence of highly ordered nanoscale spheres and stripes on the surface, in contrast to the case of higher swelling degree. The differences are explained qualitatively on the basis of polymer-solvent interaction parameters of the different components.

Synthesis and characterization of a novel biodegradable, thermoplastic polyurethane elastomer

A series of biodegradable, thermoplastic polyurethane elastomers poly (epsilon-caprolactone-co-lactide)polyurethane [PCLA-PU] were synthesized from a random copolymer Of L-lactide (LA) and epsilon-caprolactone (CL), hexamethylene diisocyanate, and 1,4-butanediol. The effects of the LA/CL monomer ratio and hard-segment content on the thermal and mechanical properties of PCLA-PUs were investigated. Gel permeation chromatography, IR, C-13 NMR, and X-ray diffraction were used to confirm the formation and structure of PCLA-PUs. Through differential scanning calorimetry, tensile testing, and tensile-recovery testing, their thermal and mechanical properties were characterized. Their glass-transition temperatures were below -8 degrees C, and their soft domains became amorphous as the LA content increased. They displayed excellent mechanical properties, such as a tensile strength as high as 38 MPa, a tensile modulus as low as 10 MPa, and an elongation at break of 1300%. Therefore, they could find applications in biomedical fields, such as soft-tissue engineering and artificial skin.