Vinyl window frames are quite popular today, but they also have a fairly negative impact on the environment. Most plastic materials are made from petroleum or natural gas, both non-renewable resources. We recently fought a war in the Mid-East over, among other things, petroleum. That war resulted in tremendous environmental damage, not to mention loss of human life. All around the world, oil spills have polluted beaches, and natural gas pipelines disrupt the countryside.
Plastics can also affect human health.
Chemically sensitive people may have an intolerance to synthetic odors given off by plastics. This is called outgassing and it is one of the causes of indoor air pollution. Outgassing will be more pronounced when a plastic window frame is heated up by sunlight, but it should decrease as a window ages. It is no wonder that fire fighters routinely wear protective breathing gear. On the plus side, vinyl window frames are often lower in price than the alternatives, they usually aren't subject to mold growth, and they require no periodic painting.