When the attraction between monomers is weaker than their attraction to the molecules of the surrounding solvent, they are called hydrophilic. Actually, this question is the only one that physicists can answer. The more specific questions about the details of polymeric interactions are for chemists and biologists. Physicists attempt to simplify complex phenomena as much as possible and thus think of polymer chains as threads, shoelaces, or necklaces made of beads on a string. These simplified models capture some essential property of a polymer.
Polymers can become entangled and form messy coils like a length of thread or a shoelace.
The excluded volume property of the monomers can be visualized as beads on a string. The next level of abstraction comes when we think about some mathematical object that can formalize our notion of a shoe lace or string of beads. The best candidate for this mathematical object is a random walk. The random walk approximation for polymers was proposed about 60 years ago by German chemist W. Kuhn. This means that the fractal dimension of a polymer chain should be two.