PET-PEG copolymers

Figure 1. Schematic of PET-PEG copolymer cross-linked by (a) glycerine, (b) sorbitol, (c) maleic anhydride, and (d) glycerine and sulfoisophthalate...

PET-PEG copolymers were synthesized by melt-condensation method with a custom made reactor [13-15]. Polymerization was carried out in two steps oligomer was prepared in the first step with DMT, EG, and PEG-200, and the oligomer made in first step was condensed and cross-linked with the agent in the second step at high temperature and high vacuum to shift reaction equilibrium further to product. Detailed synthetic procedime for PET-PEG copolymer can be found in our previous paper [13-15]. Synthetic scheme and characterization of copolymers are shown in the results and discussion section. 

Copolymer was preheated at 60°C for 24 hour to prevent any hydrolysis from moisture, and compression-molded to a sheet with 1 mm thickness and 5 mm width at 30 °C above its Tm. Sandwich-type laminate composite was prepared by compressing two 1.0 mm epoxy laminate beams and the above PET-PEG copolymer sheet in middle layer at 210 °C in a heating press. 

Figure 5. Maxmum stress and strain at break profiles of PET-PEG copolymers...

Because PET-PEG copolymer with 20 mol% of PEG 200 (E200-20) showed the best tensile test result, the composition was used for preparation of copolymer with cross-linking agent (glycerine or sorbitol) and related shape memory test (Table 1). 

Table 3 shows the similar data of PET-PEG copolymers cross-linked by MAH. Tg was affected by the MAH addition, but Tm was not. In general, Tg inereased from 8.1°C to 17.7°C when 2.5 mol% of MAH was introduced. The observed Tg inerease with the MAH addition is due to the restrieted molecular motion resulting from the increased cross-linking [16]. 

MAH is introduced, the width of rubbery plateau region above Tg increases. Because it is well known that the width increases with molecular weight, the above result confirms that MAH cross-linking increases molecular weight of the PET-PEG copolymer. Similar behavior is also observed in the intrinsic viscosity of PET-PEG-MAH copolymer (Table 3). 

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