The modification of polyethylene terephthalate(PET) by introducing polyethylene glycol (PEG) units has been studied. Copolyesters composed of ethylene glycol terephthalate/polyethylene glycol terephthalate, containing up to 20mo1e% of PEG units have been prepared by melt polycondensaction. The chemical structure of the copolyester was characterized by I.R., and the composition of it was determined by N.M.R. Thermal properties, analyzed by differential scanning calorimetry, have been discussed in terms of structure differences and particularly the effect of composition on chain flexibility. The melting temperature of the copolyester is decreased with increasing the content of PEG units in the copolyester chain, and this result is confirmed to Flory''s equation. The glass transition temperature, cold crystallization temperature, and crystallization temperature of the copolyester are decreased with increasing the content of PEG units in the chain, where the glass transition temperature is discussed with Gibbs-Di Marzio''s equation. Degree of crystallinity, measured by density, decreases with increasing the content of PEG units in the copolyester chain.

Polyethylene terephthalate의 물성개질을 위해 dimethyl terephthalate좌 ethylene glycol 외에 polyethylene glycol-400 (PEG-400)을 제 3의 단량체로 하여 PEG unit의 함량 20 mole%까지의 copolyester를 합성하였다. 적외선 분광분석과 핵자기공명 분석으로 copolyester의 구조 및 PEG unit의 함량을 분석하였으며 differential scanning calorimetry에 의해 copolyester의 구조변화에 따른 열적성질의 변화를 조사하였다. copolyester의 융점, 유리전이 온도, 저온결정화온도 및 결정화온도는 모두 PEG unit의 함량 증가에 따라 감소하였다. 특히 융점의 변화는 Flory식과 잘 일치하였고 유리전이온도의 변화는 Gibbs-Di Marzio식과 잘 부합되었으며 이로부터 PEG unit의 함량이 copolyester chain의 flexibility에 미치는 영향을 고찰할 수 있었다. 밀도측청으로부터 구한 copolyester의 결정화도 역시 PEG unit의 함량 증가에 따라 감소하였다.

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